Three-fold convolution of Bell numbers with themselves.

Terms

a(0) =1a(1) =3a(2) =9a(3) =28a(4) =93a(5) =333a(6) =1289a(7) =5394a(8) =24366a(9) =118526a(10) =618924a(11) =3456942a(12) =20573391a(13) =129951231a(14) =867877107a(15) =6106194478a(16) =45109290477a(17) =348836705235